A SID file contains a machine language music player and its music data. Goat Tracker used to be the standard cross-platform tracker, not sure if there are other options: https://sourceforge.net/projects/goattracker2/
Goattracker 2 if you want to make authentic C64 music (SID) on PC. Synder and Deflemask are two other options, but goattracker actually exports SID as a file format. This assumes you're comfortable with the tracker interface - if not, OpenMPT is a good first step, but it's good to learn since most chiptune music is made in a tracker interface as opposed to a piano roll / DAW.